Distributed Control System (hereinafter DCS) are used to control process plants and play an important role in achieving automation within the plant. The control and automation functions for the process plant are achieved by engineering these control and automation functions through the various devices of the DCS.
A method of engineering is usually based on a standard, example IEC 61499 (International Electrotechnical Commission) that specifies a system model that includes a device model, a resource model and an application model for configuring the system. The device model provides for representing devices, process interfaces, communication interfaces and also data flow for an event. Various actions can be performed on resources in the DCS. For example, the resources may be configured, parameterized, started up, deleted, and acted on through other suitable actions as desired. The resource model provides for scheduling the functions that are provided with function block specifications. The application model provides for high level application and sub-application builds and behaviour. An application may be distributed among several resources in the same or different devices.
A known engineering process includes (e.g., comprises) step of analysing inputs, building a function block network based on the inputs, connecting function blocks, and creating applications based on preset devices/controllers. The inputs can be received in the form of piping and instrumentation (P&I) diagrams, Input/Output (I/O) point description and some additional user inputs.
Each device/controller type can include a library which contains the types of Function blocks which can be used by the controller. The library can also include controller types that come with certain description of their capabilities, such as the interfaces they support for communication. These controller type libraries are provided (e.g., appear) in the engineering station toolbox. The engineer can drag or drop the function or application types into the function designers by following guidelines, which can include, for example:
1. Physical location of the field inputs and outputs and the wiring/cabling conditions.
2. Load the control logic and check at runtime the CPU utilization.
3. Communication logic configured as standard interface (Communication) blocks, connected to control logic, and shown as data or events over the control networks.
4. The number of I/Os and I/O types decide the allocations, and controllers can have access to limited I/Os or I/Os are directly attached to the controllers.
5. The engineers can select the controller types which will do the job with I/O information.
These applications are attached with timing constraints and an execution sequence is defined and downloaded to the devices so that they operate in the defined execution sequence.
In modern devices, intelligence can be included in various features of the system, such as sensors, I/Os, Controllers (Communication Interfaces or Control modules) and a Human Machine Interface (running party Real-time parts and non-real time parts), thereby creating a system that is capable of dynamic computing.
In a modern system, all data can be available on a single bus (or able to be brought to single bus via proxies and/or gateways) and the devices can be connected dynamically.
In order to exploit the capabilities of known devices and make the best of new technologies coming with newer devices having programmable intelligence and abilities for dynamic connections, there is a need for a more dynamic method for balanced application distribution across the devices in the control system.
In known systems, proximity considerations can no longer be an acceptable constraint because the wired broadband/wireless networks provide an ability to talk across long distances. Availability of all data on one bus means we can take various decisions based on the data as well as respond to the data across in a more distributed manner as well more locally. In order to efficiently distribute the data and also provide data cooperation and/or communication among the devices, the soft-marshalling/soft wiring and re-wiring on the fly should be dynamic.